1. Field of the Invention
The invention relates to a novel type of adjustable seat.
2. Discussion of the Background Art
As is known, a seat is essentially formed of a seat cushion and of a backrest, both secured to an underframe. A suitable mechanism makes it possible to adjust the inclination of the seat cushion and/or of the backrest. Adjustable seats have many applications, particularly as seats for offices, workshops, laboratories, for the disabled, for the sick, as well as in vehicles or aircraft.
These seats equipped with backrests generally call upon mechanisms formed of articulations, of springs, and of systems for locking by clamping. Although widely used, this solution has the drawback of requiring numerous components, which leads to a high cost, particularly a high assembly cost, and to a relatively large size. Moreover, it is difficult to build into these seats complementary functions such as adjustment of the damping. Finally, on an ergonomic level, the control of the locking members is generally deemed to be unsatisfactory.
Seats have also been proposed in which the inclination mechanism is controlled by electric motors. This solution, although satisfactory, is very expensive and requires the presence of a source of energy.
Document U.S. Pat. No. 2,615,499 described a chair in which each leg includes a hydrostatic system, which can slide vertically, these various hydrostatic systems being connected up in a closed circuit in pairs, respectively on the right-hand side and on the left-hand side, so as to incline the chair, respectively the seat-cushion and backrest assembly, either forward or backward. Here, the hydrostatic system which forms the actual leg, and replaces the castors or the runners, rests directly on the ground, which allows the whole seat assembly only forward or backward inclination movements, in the manner of a rocking chair.
The invention overcomes these drawbacks. It envisages a novel type of inclinable seat, which is reliable and comfortable in all positions, in which the mechanism is simple, effective, small, easy to actuate by the user and which remains of attractive cost.
This adjustable seat, formed of a seat cushion and of a backrest which are secured to an underframe and which comprises a hydrostatic mechanism for adjusting the inclination of the seat cushion and/or of the backrest, is one wherein the hydrostatic inclination mechanism bears respectively on a base arranged on the top of the underframe and on the underside of the seat cushion (or of the backrest).
In other words, the invention consists in using the hydrostatic transmission, which is moreover well known, and has been for a long time, to incline the seat cushion or the backrest, and no longer the legs themselves as is described in document U.S. Pat. No. 2,615,499 mentioned in the preamble.
As is known, a hydrostatic system is a system formed by a plurality of actuating devices connected together by pipelines filled with a fluid in equilibrium, in the manner of communicating vessels. In that way, if one of the actuating devices is lowered, the others rise in proportion through the transfer of fluid contained in the circuit. Preferably, moreover, this fluid is an incompressible fluid, such as oil or water.
In general, the actuating device is of the single-acting hydraulic actuator or flexible actuator type, in which the chamber containing the hydraulic fluid is connected to a base which is fixed onto the underframe. A hydraulic circuit of incompressible fluid connects the various chambers together. In that way, when one of the chambers lowers on one side, the chambers of the associated actuators automatically rise correspondingly, through the transfer of liquid in this circuit.
In a first advantageous embodiment, the hydrostatic system is formed of three single-acting actuators forming a triangle the base of which is arranged on the side of the rear of the seat cushion (or of the backrest), the vertical axis passing through the center of the gravity of the seat and of its load being arranged inside this triangle to ensure good equilibrium of the seat.
In another embodiment, the hydrostatic system includes six single-acting flexible actuators, arranged on either side of a bearing plate forming a base secured to the top of the underframe, namely respectively:
four actuators arranged in a square, resting under the seat cushion and on the base for the inclination of this seat cushion;
two actuators arranged under the bearing plate forming a base and on the support plate of the backrest for the inclination of this backrest.
These six actuators are connected one by one and in closed circuit to a distribution chamber.
In a preferred embodiment, the chambers of the actuators are connected together by a circuit including a shutoff member actuatable by the user, such as, for example, a tap, a locking screw or a valve, controlled by a lever, or even by any other means to control the, transfer of the liquid from one chamber to another. In an advantageous variant, the circuit may also be equipped with distributors, flow limiters, pressure accumulators or motorized pumps, depending on the additional functions which it is desired to obtain. Generally, all the known functions of hydraulic circuits may be used successfully.
In another embodiment, the seat cushion and the backrest are articulated about a horizontal spindle secured to the underframe, and the hydrostatic system, also secured to the underframe, is formed of a plurality of actuators acting respectively on the underside of the seat cushion and on the backside of the backrest, these various actuators being connected together by a common circuit in which the shutoff member is arranged so that the inclination of the seat cushion and of the backrest are synchronized when the shutoff member is open, and locked when it is closed .